Advanced polyimide materials: Syntheses, physical properties and applications

Polymer electronic memories: Materials, devices and mechanisms

An asymptotically optimum receiver designed for detecting coherent pulse trains in compound-Gaussian clutter is introduced and assessed. The proposed receiver assumes knowledge of the structure of the clutter covariance matrix, but does not require that of its amplitude probability density function (apdf). Performance is analytically evaluated, showing that the loss, as measured with respect to the corresponding optimum structure, is kept within a few dBs even for a relatively small number of integrated pulses and that it largely outperforms the matched-filter detector under all instances of practical interest. Interestingly, the proposed detector achieves constant false alarm rate (CFAR), regardless of the clutter envelope distribution and, consequently, its power. >

http://lops.perso.enseeiht.fr/papers/Conte_IEEE_TAES_1995.pdf

Asymptotically optimum radar detection in compound-Gaussian clutter

Complex elliptically symmetric (CES) distributions have been widely used in various engineering applications for which non-Gaussian models are needed. In this overview, circular CES distributions are surveyed, some new results are derived and their applications e.g., in radar and array signal processing are discussed and illustrated with theoretical examples, simulations and analysis of real radar data. The maximum likelihood (ML) estimator of the scatter matrix parameter is derived and general conditions for its existence and uniqueness, and for convergence of the iterative fixed point algorithm are established. Specific ML-estimators for several CES distributions that are widely used in the signal processing literature are discussed in depth, including the complex t -distribution, K-distribution, the generalized Gaussian distribution and the closely related angular central Gaussian distribution. A generalization of ML-estimators, the M-estimators of the scatter matrix, are also discussed and asymptotic analysis is provided. Applications of CES distributions and the adaptive signal processors based on ML- and M-estimators of the scatter matrix are illustrated in radar detection problems and in array signal processing applications for Direction-of-Arrival (DOA) estimation and beamforming. Furthermore, experimental validation of the usefulness of CES distributions for modelling real radar data is given.

Complex Elliptically Symmetric Distributions: Survey, New Results and Applications

Speckle noise is an inherent property of medical ultrasound imaging, and it generally tends to reduce the image resolution and contrast, thereby reducing the diagnostic value of this imaging modality. As a result, speckle noise reduction is an important prerequisite, whenever ultrasound imaging is used for tissue characterization. Among the many methods that have been proposed to perform this task, there exists a class of approaches that use a multiplicative model of speckled image formation and take advantage of the logarithmical transformation in order to convert multiplicative speckle noise into additive noise. The common assumption made in a dominant number of such studies is that the samples of the additive noise are mutually uncorrelated and obey a Gaussian distribution. The present study shows conceptually and experimentally that this assumption is oversimplified and unnatural. Moreover, it may lead to inadequate performance of the speckle reduction methods. The study introduces a simple preprocessing procedure, which modifies the acquired radio-frequency images (without affecting the anatomical information they contain), so that the noise in the log-transformation domain becomes very close in its behavior to a white Gaussian noise. As a result, the preprocessing allows filtering methods based on assuming the noise to be white and Gaussian, to perform in nearly optimal conditions. The study evaluates performances of three different, nonlinear filters - wavelet denoising, total variation filtering, and anisotropic diffusion - and demonstrates that, in all these cases, the proposed preprocessing significantly improves the quality of resultant images. Our numerical tests include a series of computer-simulated and in vivo experiments.

/pdf/despeckling-of-medical-ultrasound-images-4pyoujatk0.pdf

Despeckling of medical ultrasound images

A method for estimating, from cytophotometric data, the proportion of cells in three different phases of the cell cycle is proposed. Computation is done by means of determining seven parameters in the approximate function for the fluorescence intensity histogram. The proportion of cells in the GI, S, and G2-M phases, obtained by this method, was found to be reliable.

Computer Aided Analysis of Cell-Cycle Phase from Cytophotometric Histogram

Weibull-Distributed sea clutter

We fabricated Josephson junctions with the structure of Nb/Au/PI/(Pb-Bi) using an ultrathin polyimide (PI) Langmuir- Blodgett film as an electrically insulating layer with neither the presence of native oxide layers formed on the base Nb layer nor the dissolution of the base-Nb/Au electrode during the imidization of PAA (Polyamic acid long alkylamine salts) films to produce PI LB films. A typical I-V characteristic of weakly-coupled Josephson junctions was found to be obtained.

Josephson Junctions Using Polyimide Langmuir-Blodgett Films with a Nb/Au/PI/(Pb–Bi) Structure

The authors have examined the electrical properties of ultrathin insulating layers of polyimide (PI) deposited on a base of Au electrodes by using tunnel junctions with structures of Au/PI/(Pb-Bi) and Au/PI/Au. For Au/PI/Au junctions, ultrathin PI Langmuir-Blodgett films having good electrical insulating properties were obtained when the number of deposited layers was greater than about 30. It was found that the I-V characteristic of electrically insulating Au/PI/Au junctions was explained by a model on Simmons' tunnelling theory (1963), assuming that application of the top Au electrode resulted in a reduction of the PI layer thickness. For Au/Pi/(Pb-Bi) junctions, typical I-V characteristics of tunnel junctions were obtained at a temperature below the critical temperature of a superconducting Pb-Bi alloy, when the number of deposited layers was 27. It was concluded that the I-V characteristic was governed by the tunnelling conduction mechanism based on the Bardeen-Cooper-Schrieffer (BCS) theory.

Matsuo Sekine

Papers

Computer Aided Analysis of Cell-Cycle Phase from Cytophotometric Histogram

Weibull-Distributed sea clutter

Josephson Junctions Using Polyimide Langmuir-Blodgett Films with a Nb/Au/PI/(Pb–Bi) Structure

Electrical properties of polyimide Langmuir-Blodgett films deposited on noble metal electrodes

Electrical properties of polyimide Langmuir-Blodgett films sandwiched between superconducting electrodes: detection of microwaves